1. Field of the Invention
The present invention relates to a substrate for a high-frequency filter and a multiplexer used for a mobile communication apparatus and wireless device, typically for example, a mobile phone. Further, the present invention relates to a high-frequency filter and a duplexer, and more particularly, to a high-frequency filter and a duplexer using an acoustic-wave device. Furthermore, the present invention relates to a module and a communication apparatus using these.
2. Description of the Related Art
Recently, a multiband/multisystem advances for a wireless communication apparatus, typically for example, a mobile phone. A plurality of communication apparatuses are mounted to one mobile phone. One communication apparatus usually needs a plurality of filters, a duplexer, and a power amplifier. One mobile phone therefore needs to include a numerous number of high-frequency devices, and this becomes a factor for preventing the reduction in size of the mobile phone. Hence, the reduction in size and thickness of the high-frequency devices are greatly demanded.
For a high-frequency filter, a duplexer, and a power amplifier used for the communication apparatus, input/output impedances thereof are adjusted to be 50 ohms. Then, each of them is packaged in a single component and supplied. Acoustic-wave devices such as a surface acoustic wave (SAW) filter and a film bulk acoustic wave resonator (FBAR) filter are widely used for the high-frequency filter and the duplexer. Since the input/output impedance can be adjusted by the design of the filter element for the acoustic-wave devices, 50 ohms can be realized without adding another matching circuit. However, in the case of the power amplifier, the input/output impedance thereof is usually several ohms, and 50 ohms is not accomplished only by the design of the amplifier element. Therefore, matching circuit elements are required, then space therefor is necessary, and this becomes an obstacle for decreasing sizes of the components.
FIG. 18A shows an outline of an RF block of a conventional mobile phone. A high-frequency block shown in FIG. 18A comprises: an antenna 101; a duplexer 102; a low-noise amplifier (LNA) 103; an inter-stage filter 104; an LNA 105; mixers 106 and 109; low-pass filters (LPFs) 107 and 110; variable gain amplifiers (VGAs) 108 and 111; a phase control circuit 112; a transmitter 113; a inter-stage filter 114; and a power amplifier (PA) 115. FIG. 18A illustrates an RF block for structuring one communication apparatus. A multiband/multisystem mobile phone comprises a plurality of RF blocks.
Referring to FIG. 18A, the filters 114 between transmitting stages and the duplexer 102 are usually arranged in front of the power amplifier 115 and on the back thereof, respectively. Referring to FIG. 18B, the power amplifier 115 is generally provided as a power amplifier module having an amplifier element 115a and matching circuits 115b and 115c, thereby performing the impedance matching of 50 ohms between the filter and the duplexer. Therefore, the size of the power amplifier module is approximately 4×4 mm, and it is larger than a high-frequency filter (e.g., 1.4×1.0 mm). In order to reduce the size of the RF block, the simplification or deletion of a matching circuit connected to the power amplifier 115 is advantageous. Therefore, the input/output adjustable impedances of the high-frequency filter and the duplexer should be designed to be greatly smaller than 50 ohms close to the input/output impedance of the power amplifier.
However, the high-frequency filter and the duplexer are connected to the power amplifier and are also connected to another part of which the input/output impedances are usually 50 ohms. Therefore, the input/output impedances of the high-frequency filter and the duplexer need individually to be two impedances including 50 ohms and the value much smaller than 50 ohms.
Conventionally, the high-frequency filter and the duplexer having two different impedances as the input/output impedances individually have an input impedance of 50 ohms and an input impedance of 100 ohms or 200 ohms larger than 50 ohms with balance/unbalance output conversion. The filter and duplexer are realized so as to omit a balance/unbalance converting circuit existing between a low-noise amplifier and a filter, corresponding to a balanced input for reducing noises (refer to, e.g., Japan Laid-open Patent Publication No. 2001-267885).
Since the power amplifier having the input/output impedance of several ohms is generally provided as a module including a matching circuit. Therefore, the high-frequency filter and the duplexer having both the impedances of 50 ohms and a value smaller than 50 ohms are not available. However, as mentioned above, the matching circuit of the power amplifier is preferably simplified or deleted because of a demand for reducing the size of the high-frequency device. Therefore, the high-frequency filter and the duplexer having the impedance of 50 ohms and the impedance smaller than 50 ohms are needed.
Further, a duplexer 201 used for an RF block of a mobile phone shown in FIG. 19 is expected to be directly connected to a power amplifier 203 having an impedance smaller than 50 ohms and a low-noise amplifier 202 having an impedance larger than 50 ohms. Therefore, in the duplexer 201, a transmitting port 205 needs to have an input impedance smaller than 50 ohms, an antenna port 206 connected to the antenna 101 needs to have an impedance of 50 ohms, and a receiving port 204 connected to the low-noise amplifier 202 needs to have an impedance larger than 50 ohms. That is, the duplexer 201 needs to have three different impedances.
Summarily, the high-frequency filter and the duplexer individually need to have two types of impedances including the impedance smaller than 50 ohms and the impedance of 50 ohms (e.g., the inter-stage filters 114 between the transmitting stages shown in FIG. 18A), three types of the impedance smaller than 50 ohms, the impedance of 50 ohms, and the impedance larger than 50 ohms (the duplexer 201 shown in FIG. 19), or two types of impedances including the impedance of 50 ohms and the impedance larger than 50 ohms (e.g., the inter-stage filter 104 shown in FIG. 18A).
In order to manufacture the high-frequency filter and the duplexer which satisfies the specification above, the input/output impedances of filter elements including the SAW and the FBAR filters need to have each of impedance values smaller and larger than 50 ohms. Further a characteristic impedance of a transmission line disposed on a substrate on which the filter elements are disposed also need to have each of impedance values smaller and larger than 50 ohms. Since the input impedances of the SAW filter and the FBAR filter can be easily adjusted, the SAW filter and the FBAR filter have no problems.